Last Tuesday, Chicago Mayor Rahm Emanuel held a press conference to announce that he didn’t want his city’s law-enforcement authorities to follow federal requests to hold some undocumented immigrants, picked up on other charges, for deportation. The national media’s ears perked up. Emanuel, a former Chief of Staff to President Obama, was at loggerheads with his old boss — good copy in the making. But on the same day, back in Washington, D.C., much bigger news was developing on the future of federal and local cooperation on immigration policy. John Morton, the director of Immigration and Customs Enforcement (ICE), told a House subcommittee that his efforts to persuade officials to honor any of ICE’s detention requests in the jurisdiction of Cook County, which includes Chicago, had hit a wall. “I won’t sugarcoat it,” he said. “I don’t think that approach is going to work in full.”

In April, Homeland Security Secretary Janet Napolitano told Congress she was “evaluating all options” to compel Cook County, Illinois, to go along with ICE’s requests, known as “detainers,” under a program called Secure Communities, launched in late 2008 to focus immigration enforcement on criminal aliens. Morton reiterated Napolitano’s warning, but his grim assessment of the Cook County situation added further gravity to the statement: “We’ve been exploring, as the Secretary has said, our options under federal law with the Department of Justice, and we will see where that goes.” Translation: the Obama Administration has discussed the possibility of suing a jurisdiction because it’s too lax in enforcing federal immigration priorities, a mirror image of the legal drama the Administration just went through with Arizona’s law, which the Supreme Court partially struck down in June.

Some advocates have framed nondetainer policies like Cook County’s as a response to the trend of aggressive state immigration crackdowns like the one in Arizona, which requires police to try to discern a suspected undocumented immigrant’s status during a routine stop or detention. That’s convenient politics, but in a much more direct way, they are a response to the rapidly expanding federal immigration-enforcement program, Secure Communities. Under that program, local law-enforcement agents send fingerprints of detainees to the FBI and ICE, which can then ask local jails to hang on to some prisoners eligible for deportation, giving federal authorities the chance to swoop in and remove them within 48 hours. It’s a wide net, which snags serious criminals, minor offenders and otherwise law-abiding undocumented immigrants — say, someone who has failed to appear in immigration court or who has been previously deported. And it’s putting its critics, who say Secure Communities encourages local law enforcement to arrest more Latinos and undermines cooperation between police and immigrant communities, on a collision course with the Obama Administration.

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It’s not just Cook County, which stopped honoring any of ICE’s detention requests in September of last year, and the city of Chicago, which is considering a narrower ordinance directing jails not to comply with detainers for those convicted or suspected of minor offenses. On the same day that Morton testified before Congress, Washington D.C.’s city council unanimously passed a similar measure. Taos, N.M., already has one. Santa Clara County, California, has declined to honor the majority of the 1,400 ICE requests issued since October. The city of San Francisco has also declined a handful.

These figures are small compared with the vast scope of Secure Communities and the Administration’s wider immigration-enforcement efforts, which have produced more than 1.2 million deportations so far under President Obama. Since launching Secure Communities in late 2008, ICE has received 17 million sets of fingerprints, identified nearly 1 million undocumented immigrants, and deported nearly 200,000 of them. The growth of the program has been explosive. Criminal-alien removals increased 89% between 2008 and ’11, according to ICE, and more than 3,000 local jurisdictions now participate in Secure Communities, up from just 88 in 2009. ICE expects nationwide deployment in 2013.

But the number of jurisdictions resisting detention requests may soon grow too. On July 5, California’s senate passed a nondetainer policy for the entire state, which would restrict local law enforcement from going along with detainers for all but the most serious criminals. It is expected to pass the assembly next month before heading to the desk of Governor Jerry Brown, who has not said whether he will sign it. California has the largest population of undocumented immigrants in the U.S., and about 75,000 of those deported by ICE under Secure Communities have been from that state — far more than any other. It’s not clear what the Obama Administration would do if that crucial state bucked the program.

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“The Administration has to be seen as opposing [these measures] as vigorously as they did the Arizona measure,” says Jonathan Turley, a law professor at George Washington University. “First to be consistent on principle, the Administration just argued before the Supreme Court that states should not be able to create detainer policies unilaterally and that the federal government should have overriding authority in the area.”

There’s a certain irony in the Administration’s Secure Communities dilemma, even beyond the Arizona parallel. While ICE has rebuked Cook County for refusing all detention requests — and releasing 222 undocumented immigrants flagged for deportation in the process — the policies that may soon arrive in Chicago and California (which ICE also opposes) seek to prioritize the removal of hardened criminals. That’s been the Administration’s stated goal from the outset, and why Obama recently announced legal relief for some young undocumented immigrants who entered the country as children.

But it’s also why the Department of Homeland Security (DHS) insists that Secure Communities is a good idea. As congressional appropriations for immigration enforcement have ramped up — ICE’s detention and removal budget doubled between 2005 and ’09 — deportations have shot up too. DHS argues that if the money has to be spent, it’s better used going after criminals than someone else. Secure Communities isn’t as narrowly focused as its critics would like, but it’s been amended on the fly — to reduce the number of traffic violators targeted, for instance — and DHS says the portion of deportees who’ve been convicted of the most serious crimes, now 27% in the federal government’s “level 1” taxonomy, will rise over time.

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That argument hasn’t been sufficient for immigration advocates, who worry police will arrest people on pretext just so they run their prints, not to mention the spike in deportations. Many local lawmakers still insist discretion over who is held should remain with local authorities. And it’s not certain that the Administration, should it decide to pursue legal challenges to nondetainer policies, would be able to make the same case it did against Arizona. While Congress mandated information sharing in 2002, Secure Communities was established by an appropriations bill in 2008. And while Morton now describes ordinances like Cook County’s as “inconsistent with federal law,” DHS documents acquired by advocacy organizations have suggested some ambiguity as to whether federal officials always considered detainers mandatory.

“As long as it’s not directly contradicting immigration law, then it’s not pre-empted,” Steven Gonzales, a constitutional law professor at the Phoenix School of Law, says of nondetainer ordinances. “It’s a fine, fine line, but there is some logic there.” Turley, of George Washington University, says there’s a crucial difference between taking unilateral action, like Arizona did, and declining to carry out federal requests. “I think it would be very difficult for the Justice Department to argue that states are impeding federal policy by not agreeing to be agents of that policy … that would be a serious threat to federalism and states’ rights.”

If legal action isn’t a credible threat, cutting off federal funds just might be. The Justice Department reimburses local jails for a part of the cost of holding detainees flagged for deportation, and provides a number of other law-enforcement grants. Morton hinted in his testimony that some of that funding may be subject to re-evaluation. “The power of the purse is definitely the strongest power that the government has,” says Aarti Kohli, a senior fellow at Berkeley’s Chief Justice Earl Warren Institute on Law and Social Policy. But Kohli is skeptical the Administration would even take things that far. “Politically, I don’t see what’s to be gained,” she says. It is always risky to snatch away federal funds in an election year.

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If nondetainer policies move ahead and the Obama Administration doesn’t attempt to force jurisdictions to comply, Secure Communities is sure to be another piece of patchwork in the U.S.’s already mottled immigration policy.

The Cook County sheriff, Tom Dart, who says he doesn’t like having to release some of the detainees who’ve been flagged for deportation but has given up trying to persuade his county board and ICE to work things out, found the program to be inconsistent to begin with — its guiding principles impossible to discern. “We have this hodgepodge of rules and laws when it applies to detainers,” he says. “It was so ambiguous, the whole thing.” Ambiguity is a word he used more than once to describe the challenges of immigration enforcement.

That’s the way things are. Neighboring Arizona and California could soon have vastly different protocols for arresting undocumented immigrants and turning them over to federal authorities. “It really is a political issue, a struggle between different points of view,” says Gonzales. “And as long as Congress remains polarized and unable to move forward on comprehensive immigration reform, there are going to be leaks all over the ship … depending on what political environment you’re in around the country.”